Cerebrovascular disease increased gradually in recent years, and is a second disease in cause of death in China that found by epidemiological researcher. In China, there are 1.3 to 1.5 million of new cerebrovascular disease cases, 6 to 7 million of the total number of sick people, while people died from cerebrovascular disease are nearly 1 million each year, about ¾ of the survivors of are different degrees of incapacity, severe disability in 40% or more. The cerebrovascular disease has a higher morbidity, and is serious harm to human health and quality of life, which result in social and economic of hospitals, physicians, rehabilitation, pharmacy, and indirect consumption of up to 30 billion yuan per year. People dying from the ischemic stroke (cerebral infarction) disease accounts for 70% of the people that died from cerebrovascular disease, therefore, the study of cerebral infarction is very important.
Every state guideline recommends that the ischemic stroke in the ultra-super-early (within 3 hours) is preferredly healed by thrombolytic therapy of intravenous recombinant tissue-type plasminogen activator (rt-PA). However, the number of patients with ischemic stroke healed by hyperacute thrombolytic therapy is less than 1% in China. According to statistics, patients of hyperacute ischemic healed by rt-PA treatment are only 409 of the whole of China in 2004. Compared to newly issued 1.3 million of patients with ischemic stroke, the number of patients of hyperacute ischemic healed by rt-PA treatment is undoubtedly shocking. In the United States, there are at least 0.7 million new cases of ischemic stroke, but only 1% can be healed by thrombolytic therapy. This phenomenon is largely caused by that thrombolytic therapy is prone to bring other serious complications. Therefore, patients must be cured strictly in accordance with pathological state of the brain. However, how to understand the pathological state of patient is a difficulty of medicine, which is difficult to overcome.
For a long time, how to make the early diagnosis of ischemic stroke, determination of ischemic penumbra and effective implement for cerebral protection, saving of the damaged nerve function of the ischemic penumbra, have been the main treatment direction for ischemic stroke. Astrup J. et al present a concept of ischemic penumbra guides in 1981. The theory of ischemic penumbra guides shows that cerebral ischemia induces existence of a central necrosis area and a penumbra area surrounding the central necrosis area. The penumbra area losses neurological function, but nerve cells of the penumbra are still alive. At this point, if reperfusion active thrombolytic treatment is valid in a time window, most brain cells still prevent ischemic necrosis. The main purpose of thrombolysis is to save the ischemic penumbra area, restore tissue blood supply, and improve clinical symptoms. Therefore, presence of the ischemic penumbra area is a basic condition for thrombolytic therapy.
The ischemic penumbra and the central necrosis are a dynamic process of the pathophysiology, which is closely related to ischemia time, vascular occlusion and collateral circulation. With aggravation of ischemia and prolonged ischemia time, the central necrotic area is gradually expanded, the ischemic penumbra area is gradually shrunk. Therefore, the time window of reperfusion of the thrombolytic therapy is strict, over the time window of reperfusion may aggravate cerebral edema and brain cell damage, and increase mortality. A study researched by Absett et al shows that continuous treatment of 400 patients in 6 hours time window, the number of patients cured within 3 hours is only 10%, the number of patients cured within 3-6 hours is accounted for 90% of all cases, the number of patients cured within 5-6 hours is also accounted for 50% of all cases. Therefore, within the super-acute phase which is called the “time is brain”, the number of patients benefited from thrombolytic therapy will grow exponentially at each extended hour. Thrombolytic therapy determines whether the ischemic penumbra area is existed and whether vascular barrier through the guidance of imaging damaged, and is no longer calculated in accordance with the onset of reperfusion time window, which extends the reperfusion time window and increase the number of patients accepted thrombolytic therapy. Practice of medicine shows that the radiographic can recognize the ischemic penumbra area to guide clinical treatment, and obtain satisfactory results in the traditional treatment time window. By the radiographic guidance, ten thousands of patients of peracute ischemic stroke can benefit from the thrombolytic therapy each year.
At present, the ischemic penumbra area is determined by a combination of magnetic resonance diffusion weighted imaging and magnetic resonance perfusion weighted imaging. The diffusion weighted imaging is referred to as DWI. The perfusion weighted imaging is referred to PWI. High signal abnormal area of the diffusion weighted imaging (DWI) represents a cerebral infarction area. Perfusion abnormal area of the PWI represents a damaged area. A unmatch area between the PWI and the DWI is a possible ischemic penumbra area, which is defined the difference between the perfusion abnormal area of the PWI and the high signal abnormal area of the DWI. PWI>DWI is considered as the best way of clinical thrombolysis guideline.
However, the above model has the following serious shortcomings:
(1) The PWI requires injection of contrast agent, which is a relative measurement because different scanning machines have no uniform standard.
(2) The perfusion abnormal area of the PWI in accordance with qualitative analysis, and calculation time of the perfusion abnormal area is rather time-consuming. Furthermore, this brain flow model is still controversial, and the magnetic resonance perfusion weighted imaging do not pass the U.S. Food and Drug Administration (FDA) approval, such that this brain flow model may be have a clinical risk.
(3) The DWI is not only dependent on the dispersion characteristics, but also on the a T1 weighted, a T2 weighted and a proton density, especially on the T2-weighted.
(4) The actual ischemic penumbra area is usually smaller than the unmatch area of PWI/DWI. An error between the actual ischemic penumbra area and the unmatch area is up to 40%-60%.
(5) A difficulty of determining the infarction area, the ischemic penumbra area by PWI/DWI is a significantly different of diffusion and perfusion characteristics of different brain tissue (gray matter and white matter). The significantly difference can be up to 20%. If the significantly difference does not distinguish, there will be bring principle error.
In view of inherent weaknesses of the PWI and unmatch difficulty of the PWI/DWI, Prosser et al. advance a ischemic penumbra band model of clinical unmatch in accordance with the DWI, but the ischemic penumbra band model of clinical unmatch can be only achieved 53% of sensitivity.
Therefore, a method and system for obtaining brain characteristic parameters, a thrombolysis decision guideline system and method thereof are desired in order to overcome the above-described shortcomings.